Juventus' Mario Mandzukic celebrates scoring their second goal with Cristiano Ronaldo.
Juventus, chasing an eighth successive title, have six points from two games after a somewhat fortunate win, but Ronaldo is still waiting for his first goal since his move from Real Madrid.
Lazio - fifth last season - have had their worst start in over a decade following last weekend's 2-1 defeat at home against Napoli.
Joao Cancelo's low cross from the right was partially intercepted by Lazio goalkeeper Thomas Strakosha but he only succeeded in pushing the ball onto Ronaldo's foot.
Marco Parolo should have equalised for Lazio in the first-half stoppage time with a free header inside the box but guided his effort over the crossbar following a pin-point cross into the area by Sergej Milinkovic-Savic.
The Portuguese skipper has scored many goals in his career but revealed that the best so far was the one he netted against his current side Juventus in the Champions League semifinals last season, "It was the best goal in my career so far. Ronaldo understands that and he is settling in very well", said Juventus coach Massimiliano Allegri.
"At first, we played in a hurry. We needed these characteristics in midfield today", he said.
"We went from being frenetic at times to falling asleep at others".
Giacomo Bonaventura sensationally opened for Milan after 15 minutes in the San Paulo Stadium with a Davide Calabria half-volley giving the visitors a two-goal advantage four minutes after the break.
There was another big cheer shortly afterwards when former Napoli striker Higuain shot high and wide from his only real opening of the match.
Juve left it late against Chievo last weekend, and have substitute Federico Bernardeschi to thank after tucking away a stoppage-time victor to give the Old Lady a 3-2 win.